RoseStreet Labs Energy

Phoenix, AZ, United States

RoseStreet Labs Energy

Phoenix, AZ, United States
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Chen G.,Lawrence Berkeley National Laboratory | Chen G.,Huaiyin Normal University | Yu K.M.,Lawrence Berkeley National Laboratory | Reichertz L.A.,Lawrence Berkeley National Laboratory | And 2 more authors.
Applied Physics Letters | Year: 2013

We have studied structural, electrical, and optical properties of sputter deposited ternary CdMgO alloy thin films with total Mg concentration as high as 44%. We found that only a fraction (50%-60%) of Mg is incorporated as substitutional Mg contributing to the modification of the electronic structures of the alloys. The electrical and optical results of the Cd1-xMg xO alloys are analyzed in terms of a large upward shift of the conduction band edge with increasing Mg concentration. With the increase of the intrinsic bandgap, appropriately doped Cd-rich CdMgO alloys can be potentially useful as transparent conductors for photovoltaics. © 2013 AIP Publishing LLC.


Tanaka T.,Saga University | Tanaka T.,Japan Science and Technology Agency | Yu K.M.,Lawrence Berkeley National Laboratory | Levander A.X.,Lawrence Berkeley National Laboratory | And 8 more authors.
Japanese Journal of Applied Physics | Year: 2011

We report the optical properties of ZnTe1-xOx (ZnTeO) and evidence for the photovoltaic (PV) activity of a ZnTeO intermediate band solar cell (IBSC). By photomodulated reflectance measurements, electron transitions from the intermediate band to the conduction band were demonstrated. The optical absorption coefficients for the electron transition from the valence band to the intermediate band exceeds 2 × 104 cm -1, suitable for thin-film PV device applications. The ZnTeO IBSC exhibits an enhanced spectral response below the band edge of ZnTe, and all results are consistent with the proposed conversion mechanism of IBSC. © 2011 The Japan Society of Applied Physics.


Gherasoiu I.,RoseStreet Labs Energy | Yu K.M.,Lawrence Berkeley National Laboratory | Reichertz L.A.,Lawrence Berkeley National Laboratory | Kao V.M.,Lawrence Berkeley National Laboratory | And 4 more authors.
Physica Status Solidi (B) Basic Research | Year: 2010

Using plasma-assisted molecular beam epitaxy (PA-MBE), high quality InxGa1-xN layers with x in the range from 25 to 31% have been grown on silicon (111) substrates. The polarity of the layers has been found to impact the incorporation of In, with Ga polar buffers promoting the deposition of uniform composition InGaN. We have achieved films with indium fraction up to 31% and rocking curve width of 538 arcsec. Residual donor concentration as low as ~1.2×1018cm-3 was measure in these films, suggesting that p-type doping with Mg can be achieved. The presence of AlN layers and the increasing thickness of the GaN buffer do not appear to have a significant contribution to the series resistance of the structure. The investigation of the InGaN layers by X-ray diffraction did not reveal any significant phase separation occurring during the MBE deposition although the photoluminescence spectrum exhibits low energy features that would require further investigation. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Gherasoiu I.,RoseStreet Labs Energy | Yu K.M.,Lawrence Berkeley National Laboratory | Reichertz L.A.,RoseStreet Labs Energy | Reichertz L.A.,Lawrence Berkeley National Laboratory | And 2 more authors.
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2014

Magnesium is the only known effective p-type dopant for nitride semiconductors. Although the p-doping is challenging for AlN and GaN, requiring the activation of the Mg acceptors, in the case of the MOCVD growth, methods for obtaining reliable and high level doping have been developed. Similarly for n-type doping silicon has been used successfully for more than a decade. More recently germanium has been found to be as effective for n-type doping, with the additional advantage of inducing less strain in the host lattice due its size similarity to gallium. Doping of InGaN is more challenging due the difficulty in controlling the donor background associated with material extended defects and the incorporation of impurities. Although successful p-type doping of InGaN with Mg has been demonstrated, quantitative limits for the magnesium incorporation and its behavior have not been analyzed. In this paper we investigate both, Mg and Ge doping of InGaN. We also discuss the challenges posed by the growth and measurement of the InGaN pn-junctions characteristics as well as we demonstrate the fabrication of large area long wavelength LEDs on silicon (111) by PA-MBE. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Tanaka T.,Lawrence Berkeley National Laboratory | Tanaka T.,Saga University | Yu K.M.,Lawrence Berkeley National Laboratory | Stone P.R.,Lawrence Berkeley National Laboratory | And 9 more authors.
Journal of Applied Physics | Year: 2010

We report on the proof of photovoltaic activity of homojunction ZnTe solar cells in which n-ZnTe layers are fabricated by thermal diffusion of Al into p-ZnTe at several diffusion times to control the junction depth. An open circuit voltage of approximately 0.9 V was obtained under 1× sun AM1.5G condition in all solar cells, independent of diffusion times, while a short circuit current dropped down with increasing the diffusion time due to an increased light absorption in heavily defective Al-diffused layer. These fundamental results provide a basis for future development of intermediate band solar cells based on ZnTe materials. © 2010 American Institute of Physics.


Hoffbauer M.A.,Los Alamos National Laboratory | Williamson T.L.,Los Alamos National Laboratory | Williams J.J.,Los Alamos National Laboratory | Fordham J.L.,Los Alamos National Laboratory | And 3 more authors.
Journal of Vacuum Science and Technology B:Nanotechnology and Microelectronics | Year: 2013

A number of In-rich InGaN films with In contents in the 20-40% range have been grown at moderately low temperatures on sapphire and silicon substrates at high growth rates using a versatile molecular beam epitaxy-type technology that utilizes an energetic beam of N atoms called energetic neutral atom beam lithography and epitaxy to overcome reaction barriers in the group III-nitride system. Extensive characterization results on the crystalline, optical, and electrical properties of the In-rich InGaN materials are reported. It was found that N-rich growth conditions are required to produce materials that have excellent crystallinity, uniform compositions, and bright band edge photoluminescence. For In-rich InGaN growth on sapphire, electrical transport measurements show reasonably low carrier concentrations and high mobilities. Successful p-type doping of In-rich InGaN with ∼20% and ∼40% In contents is demonstrated, and preliminary results on the formation of a p-n junction are reported. For In-rich InGaN growth on Si, the film structural properties are somewhat degraded and carrier concentrations are considerably higher. © 2013 American Vacuum Society.


Tanaka T.,Lawrence Berkeley National Laboratory | Tanaka T.,Saga University | Yu K.M.,Lawrence Berkeley National Laboratory | Stone P.,Lawrence Berkeley National Laboratory | And 9 more authors.
Conference Record of the IEEE Photovoltaic Specialists Conference | Year: 2010

We describe the fabrication of ZnTe1-xOx intermediate band solar cell (IBSC) using the combination of oxygen ion implantation and pulsed laser melting. Also, we report the first demonstration of homojunction ZnTe solar cells in which n-ZnTe layer is fabricated by thermal diffusion of Al into p-ZnTe. The preliminary results of the ZnTe1-xOx IBSC are compared with the ZnTe cell. The homojunction ZnTe solar cells exhibited photovoltaic activity with an open circuit voltage of approximately 0.9 V and a maximum short circuit current (JSC) of 1.75 mA/cm2. J SC was found to depend strongly on the location of pn-junction, with shallower pn-junction depth, corresponding to higher JSC. Photo-modulated reflectance spectra of ZnTe1-xOx, show two optical transitions from the valence band to the conduction subband E + (∼2.5 eV) and from the valence band to the intermediate band E- (∼1.7 eV). The external quantum efficiency of ZnTe 1-xOx solar cell clearly shows PV responses due to the transition from valence band to the two conduction subbands (E- and E+) demonstrating the photovoltaic action through the intermediate band in this highly mismatched alloy. © 2010 IEEE.


Tanaka T.,Saga University | Tanaka T.,Japan Science and Technology Agency | Yu K.M.,Lawrence Berkeley National Laboratory | Levander A.X.,Lawrence Berkeley National Laboratory | And 8 more authors.
Conference Record of the IEEE Photovoltaic Specialists Conference | Year: 2011

Optical properties of ZnTe 1-xO x (ZnTeO) and evidence for the photovoltaic (PV) activity of a ZnTeO intermediate band solar cell (IBSC) are reported. Electron transitions from the intermediate band to the conduction band were observed by photomodulated reflectance measurements. The optical absorption coefficients for the electron transition from the valence band to the intermediate band exceeds 2 × 10 4 cm -1, suitable for thin film PV device applications. The ZnTeO IBSC exhibits an enhanced spectral response below the bandedge of ZnTe, and all results are consistent with the proposed conversion mechanism of IBSC. © 2011 IEEE.

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